New Zealand strong-motion network development plan 1999-2009

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Cousins, W.J.; McVerry, G.H. 2009 New Zealand strong-motion network development plan 1999-2009. Lower Hutt, N.Z.: GNS Science. GNS Science report 2009/44 40 p.

Abstract: The aims of strong-motion earthquake recording are discussed, and a plan is developed for installing a network of accelerographs throughout New Zealand so as to meet those aims in an optimal manner. Of prime importance is the need to record strong ground shaking on all types of ground underlying urban New Zealand, especially in the epicentral regions of earthquakes of magnitude 7 or greater. Thus the network needs to have many recorders within 5 – 10 km of the most active faults in New Zealand, on various classes of ground, especially in at-risk urban areas. Given that urban Wellington Region clearly constitutes the worst earthquake risk in New Zealand it is a priority location. It is not that we want to experience the Wellington Fault earthquake, but rather the need is to characterise the soils and buildings of urban Wellington in order to best prepare for it. The next highest levels of risk are in the south-eastern part of the North Island (Palmerston North to Napier) and around Christchurch. Arrays of instruments (a) beneath the ground in soft soils, and (b) on the surface over hills and ridges, will enable a variety of phenomena to be studied with confidence, including the amplification of shaking by soft soils and the topographic enhancement of shaking by certain land forms. The recorded behaviour of engineered structures is important for calibrating the seismic design process. It is sobering to realise that no New Zealand building of four or more storeys, designed in accordance with any earthquake code, has yet been tested in strong earthquake shaking. A range of building types needs to be included, covering current and superseded design methods, low- to high-rise, a variety of conventional structural types, and modern specialist designs. The work described here is largely retrospective in that it builds on earlier unpublished plans that, since 1999, have guided the strong-motion component of the GeoNet Project at GNS Science. From a strong-motion point of view the installation process has occurred in three phases, viz. (i) free-field sites with emphasis on near-fault locations, microzonation, and country-wide coverage, (ii) the strong-motion component of the National Seismograph Network upgrade, and (iii) arrays in buildings and other structures. Phases (i) and (ii) are largely compete, phase (iii) is in progress. A fourth phase is likely to include the upgrading of obsolete or substandard instruments, and improving coverage in selected areas as recommended by a recent review of the GeoNet Project. (auth)